December 17, 2004

Cassini Examines Saturn’s Moon, Dione

LOS ANGELES (AP) -- The Cassini spacecraft's close flyby of Saturn's mysterious moon Titan this week revealed clouds that will give clues to its weather, but the pass left scientists still puzzled about its surface.

A flyby of another of the ringed planet's many moons, Dione, produced more immediate rewards: It revealed that wispy features long thought to be ice deposits are actually tectonic fractures that have left ice cliffs.

The findings were released Thursday by members of the mission's science team during a telephone news conference at the fall meeting of the American Geophysical Union in San Francisco.

"This week has been the tale of two moons," imaging scientist Carolyn Porco said. "One of them has been like out of a Lewis Carroll story and gets curiouser and curiouser the more we look at it and the closer we get, and the other turns out to be gloriously clear and has given us what I consider to be one of our most surprising results so far."

Dione and Saturn

In the above image, Cassini captured Dione against the globe of Saturn as it approached the icy moon for its close rendezvous on Dec. 14, 2004. This natural color view shows the moon has strong variations in brightness across its surface, but a remarkable lack of color, compared to the warm hues of Saturn's atmosphere. Several oval-shaped storms are present in the planet's atmosphere, along with ripples and waves in the cloud bands.

The images used to create this view were obtained with the Cassini spacecraft wide-angle camera at a distance of approximately 603,000 kilometers (375,000 miles) from Dione through a filter sensitive to wavelengths of ultraviolet light centered at 338 nanometers. The Sun-Dione-spacecraft, or phase, angle is 34 degrees. The image scale is about 32 kilometers (20 miles) per pixel.

Dione Mapping

This map of Saturn's moon Dione, generated from Cassini images taken during the spacecraft's first two orbits of Saturn, illustrates the imaging coverage planned during Cassini's first Dione flyby on Dec. 14, 2004.

Colored lines enclose regions that will be covered at different imaging scales as Cassini approaches Dione.

Cassini will zoom past Dione at a distance of approximately 81,400 kilometers (50,600 miles) during this flyby. An even closer encounter with Dione is in store for Cassini in October 2005, when the spacecraft is slated to fly past the icy moon at a mere 500 kilometers (311 miles).

Images from this week's flyby will be superior in resolution to those obtained by NASA's Voyager 1 in November 1980. Voyager 1 passed Dione at a distance of 161,520 kilometers (100,364 miles) at closest approach, yielding a best resolution of approximately 1 kilometer per pixel.

The area to be imaged at highest resolution by Cassini during this upcoming flyby will be centered on the bright, wispy terrain on Dione's trailing hemisphere, marked by the red outline on this map. The resolution of Cassini images in this region will be 500 meters per pixel and better.

The map was created by images acquired in visible light using the Cassini narrow angle camera. The highest southern latitudes on Dione have not yet been seen by Cassini, resulting in the map's lower limit of approximately 80 degrees south latitude.

Dione Closeup

This incredible, high resolution view of Saturn's moon Dione was taken during Cassini's first close approach to the icy moon on Dec. 14, 2004. The view shows linear, curving features within the region of the bright wispy terrain Dione is known for.

The image was obtained in visible light with the Cassini spacecraft narrow angle camera at a distance of approximately 156,000 kilometers (97,000 miles) from Dione. The Sun-Dione-spacecraft, or phase, angle is 34 degrees. The image scale is about 1 kilometer (0.6 miles) per pixel.

Dione's Surprise

As it zoomed in on Saturn's moon Dione for a close flyby, the Cassini spacecraft captured a set of images of the icy moon which have been combined into a mosaic here to provide a stunningly detailed global view.

Five narrow angle frames comprise this view of the `wispy terrain' on the anti-Saturn side of Dione. To the surprise of Cassini imaging scientists, the wispy terrain does not consist of thick ice deposits, but rather the bright ice cliffs created by tectonic fractures. The surface is also clearly very heavily cratered. The image scale is 0.9 kilometers (0.6 miles) per pixel; the phase angle is 34 degrees.

Highest Resolution image of Dione

This very detailed image taken during the Cassini spacecraft's closest approach to Saturn's moon Dione on Dec. 14, 2004 is centered on the wispy terrain of the moon. To the surprise of Cassini imaging scientists, the wispy terrain does not consist of thick ice deposits, but rather the bright ice cliffs created by tectonic fractures.

About Cassini

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging team is based at the Space Science Institute, Boulder, Colo.


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